1. Field of the Invention
The present invention relates to a magnetoresistive sensor for detecting a magnetic field by utilizing the magnetoresistance effect. More particularly, the present invention relates to a magnetoresistive sensor that is capable of narrowing an effective track (read) width and is adaptable for higher recording density, and to a method for manufacturing the magnetoresistive sensor.
2. Description of the Related Art
FIG. 28 is a sectional view of a conventional magnetoresistive sensor, looking from the side facing a recording medium.
In the magnetoresistive sensor shown in FIG. 28, a lower gap layer 9 is formed on a lower shield layer 8, and an antiferromagnetic layer 11 is formed on the lower gap layer 9 to extend in the X-direction (as shown in the figure), with an underlying layer 10 interposed between the two layers 11 and 9. The antiferromagnetic layer 11 is projected upwardly at a height d1 along its central area (as viewed in the X-direction). A pinned magnetic layer 12, a nonmagnetic electrically conductive layer 13, a free magnetic layer 14, and a protective barrier layer 15 are successively formed in that order on the projected area of the antiferromagnetic layer 11. As a result, a multilayered film 16 is formed by the stack from the underlying layer 10 to the protective barrier layer 15.
The antiferromagnetic layer 11 is formed of an antiferromagnetic material, such as a Pt—Mn (platinum-manganese) alloy. The pinned magnetic layer 12 and the free magnetic layer 14 are each formed of, e.g., a Ni—Fe (nickel-iron) alloy, Co (cobalt), a Co—Fe (cobalt-iron) alloy, or a Co—Fe—Ni alloy. The nonmagnetic electrically conductive layer 13 is formed of a nonmagnetic electrically conductive material having low electrical resistance, such as Cu (copper).
As shown in FIG. 28, metal films 17, each of which is formed of, e.g., Cr, and which serve as a buffer film and an alignment film, are formed on areas indicated by a width T8 of the antiferromagnetic layer 11 extending in the X-direction such that the metal films 17 cover respective opposite lateral surfaces of the pinned magnetic layer 12, the nonmagnetic electrically conductive layer 13 and the free magnetic layer 14. The formation of the metal films 17 help to increase the bias magnetic field generated by hard bias layers 18 (described below).
The hard bias layers 18 of, for example, a Co—Pt (cobalt-platinum) alloy or a Co—Cr—Pt (cobalt-chromium-platinum) alloy, are formed on the metal films 17.
The hard bias layers 18 are magnetized in the X-direction (track-width direction). With the bias magnetic field generated by the hard bias layers 18 in the X-direction, magnetization of the free magnetic layer 14 is aligned in the X-direction.
Also, intermediate layers 19 of a nonmagnetic material, such as Ta, are formed on the hard bias layers 18, and electrode layers 20 of, for example, Cr, Au, Ta or W, are formed on the intermediate layers 19.
Further, an upper gap layer 21 of an insulating material is formed on both the multilayered film 16 and the electrode layers 20, and an upper shield layer 22 of a magnetic material is formed on the upper gap layer 21.
In the above-mentioned structure, the width of an upper surface of the multilayered film 16 on which the electrode layer 20 is not formed defines an optical track width O-Tw, and the distance between the upper shield layer 22 and the lower shield layer 8 at a position which is aligned with the center of the multilayered film 16 defines a gap length G1.
With the recent progress toward higher recording densities of magnetic recording mediums, the demand for further reducing the gap length G1 of magnetoresistive sensors has increased for the purpose of increasing linear recording density. To reduce the gap length G1, the film thicknesses of the lower gap layer 9 and the upper gap layer 21 must be decreased.
In the structure of the conventional magnetoresistive sensor shown in FIG. 28, however, the surface on which the upper gap layer 21 is formed includes a step (level difference) formed by a lateral surface 20a of the electrode layer 20a relative to a surface 16a of the multilayered film 16. The insulating material used for forming the upper gap layer 21 is difficult to deposit on such a step. Accordingly, as the film thickness of the upper gap layer 21 is reduced, and while the step remains formed as described above, the upper gap layer 21 becomes more difficult to deposit on the step, and the risk of a short-circuit is more likely to occur between the upper shield layer 22 and the electrode layer 20.
As another problem, there occurs a phenomenon that magnetic fields generated from recording tracks of a recording medium, which are positioned on both sides of a recording track under detection, enter the magnetoresistive sensor and are detected in areas near opposite ends of the multilayered film 16. Such a phenomenon is negligible when the track width of the magnetoresistive sensor and the track pitch are relatively wide, e.g., when the track width is not less than 0.2 μm. At a track width of less than 0.2 μm, however, the track pitch is narrowed correspondingly and a ratio of the magnitude of magnetic fields entering from the recording tracks on both sides to the magnitude of magnetic field generated by the recording track under detection is increased. This leads to a phenomenon that the effective track width is larger than the optical track width O-Tw, and hence, the magnetoresistive sensor is not adaptable for higher recording density of a recording medium.